Optical fiber array and method of making the same

ABSTRACT

An optical fiber array includes a pair of blocks having respective recesses which, when the blocks are combined together, cooperate together to define a cavity, and a plurality of optical fibers having respective end portions accommodated within the cavity in a linear array. Neighboring end faces of the blocks adjacent end faces of the optical fibers are ground at an inclination relative to a common plane in which the linear array of the end portions of the optical fibers lie and also relative to an optical axis of each of the optical fibers. A method of making the optical fiber array and a wavelength selecting device utilizing the optical fiber array are also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates a method of arranging the form of a lineararray, a plurality of optical fibers of a kind generally used in opticalfiber communication and information processing, a method of fixing theoptical fibers in readiness for connection with a corresponding numberof similar optical fibers, and a wavelength selecting device utilizingthe optical fibers.

2. Description of the Prior Art

Requirements associated with the linear arrangement of optical fibersand the positioning accuracy thereof have now become severe and, at thesame time, various attempts have been made to minimize problems broughtabout by rays of light reflected from end faces of the optical fibersconnected with other optical elements. Although the problems broughtabout by the reflection of light from the end faces of the opticalfibers may be substantially eliminated if the end face of each opticalfibers is skewed, the optical fibers now in wide use have an end facelying perpendicular to the longitudinal axis thereof.

Hereinafter, one example of the prior art methods of making theconventional linear array of optical fibers referred to above will bediscussed.

FIGS. 8(a) and 8(b) are schematic diagrams showing the sequence ofmanufacture of the conventional optical fiber array, and FIG. 9 is aschematic perspective view of the optical fiber array manufactured bythe method shown in FIGS. 8(a) and 8(b). Referring to FIGS. 8 and 9,reference numerals 111 and 112 represent respective blocks; referencenumerals 121 and 122 represent guide grooves defined in the associatedblocks, respectively; and reference numeral 130 represents a pluralityof optical fibers.

The optical fiber array is manufactured in the following manner.

The optical fibers 130 are received in the guide grooves 121 defined inthe block 111 so as to be spaced an equal distance from each other asshown in FIG. 8(a). In order to fix the optical fibers 130 in positionwithin the guide grooves 121, the block 112 having the guide grooves 122defined therein in a pattern matching that of the guide grooves 121 inthe block 111 is placed from above onto the block 111 as shown in FIG.8(b). In this way, the optical fibers 130 are firmly clamped between theblocks 111 and 112.

While the optical fibers 130 are clamped between the blocks 111 and 112,end faces of those optical fibers 130 are ground to complete the opticalfiber array as shown in FIG. 9. In this connection, see, for example, apaper by J. Lipson et al. entitled "A Six-channel Wavelength Multiplexerand Demultiplexer for Single Mode Systems" (IEEE Journal of LightwaveTechnology, LT-3, No. 5, Page 1159, 1985).

However, the above-discussed prior art method has a problem in that ahighly precise machining technique is required in forming the equallyspaced guide grooves 121 or 122 in each of the blocks 111 and 112; also,the spacing between each of neighboring ones of guide grooves 121 or 122is required to be small. Where the plural optical fibers 130 arerequired to be closely juxtaposed with the minimized spacing betweenneighboring optical fibers, a more precise positioning accuracy isrequired. In addition, when stresses are induced between the opticalfibers 130 and end faces of the guide grooves 121 and 122 during thepositioning of the optical fibers 130, breakage or damage tends to occurat such portions of the optical fibers where the stresses are induced.

Moreover, since the respective end faces of the optical fibers areperpendicular to the associated optical axes thereof, rays of lightreflected from those end faces of the optical fibers bring about anadverse influence upon optical elements with which they are to beconnected. Yet, even though the optical fibers having inclined end facesare made available, it has been difficult to arrange them at a preciselyground angle.

The prior art wavelength selecting device will now be discussed. Thewavelength selecting device is a device for selecting a particular lightfrom the multiplexed light beams used in a wavelength multiplexedoptical communication system and, in recent years, various types ofwavelength selecting devices have been suggested and examined.Specifically, a wavelength selecting method utilizing a diffractiongrating is generally effective to accomplish a highly accuratewavelength selection at a broad band.

One example of the prior art wavelength selecting devices will now bespecifically discussed.

FIG. 11 pertains to the structure of the prior art wavelength selectingdevice, wherein FIGS. 11(a) and 11(b) depict top plan and side viewsthereof, respectively. In FIG. 11, reference numeral 41 represents aninput optical fiber; reference numeral 42 represents a light receivingoptical fiber; reference numeral 43 represents a lens; reference numeral44 represents a diffraction grating; reference numeral 45 represents arotary mechanism; and reference numeral 46 represents an end face ofeach of the optical fibers 41 and 42.

The wavelength selecting device operates in the following manner. Forthe purpose of discussion, the wavelengths are respectively designatedby λa, λb and λc in the order from the shortest wavelength.

Wavelength multiplexed beams having the respective wavelengths λa, λband λc emitted from the input optical fiber 41 are incident on thediffraction grating 44 through the lens 43 and are subsequentlydiffracted by the diffraction grating 44. Some of the diffracted beamsfalling in a desired wavelength region are converged by the lens 43 soas to enter the light receiving optical fiber 42, thereby accomplishinga wavelength selection. Specifically, when the diffraction grating 44while receiving the wavelength multiplexed beams is rotated by therotary mechanism 45, the beams of respective wavelengths λa, λb and λccan be directed into the light receiving optical fiber 42.

In the construction described above, however, the end face 46 of each ofthe optical fibers 41 and 42 is ground so as to lie perpendicular to theoptical axis of the respective optical fiber 41 or 42 and, therefore,the reflected light tends to be multiply reflected between the two endfaces of the input and light receiving optical fibers 41 and 42 and,hence, between a transmitter side and a receiver side, causing aFabry-Perot resonance. The occurrence of the Fabry-Perot resonance oflight tends to adversely affect the quality of transmitted signalsparticularly in the case of analog transmission.

Also, since the input optical fiber 41 and the light receiving opticalfiber 42 are arranged in the same direction as the direction ofdiffraction of the rays of light from the diffraction grating 44, and ifthe wavelength multiplexed beams contain a light component of awavelength whose angle of diffraction matches the direction of the inputoptical fiber, the light of such wavelength tends to be coupled to theinput optical fiber, bringing about an adverse influence on atransmitter as a back-reflected light. This problem is inherent in, forexample, the device disclosed in U.S. Pat. No. 4,763,969.

SUMMARY OF THE INVENTION

Objects of the present invention are to provide an improved opticalfiber array, and a method of making the same, wherein the interval orpitch at which a plurality of optical fibers are laid down in a lineararray is minimized to a value comparable to the outer diameter of eachoptical fiber, which does not require the use of a highly sophisticatedmachining or grinding technique when arranging the optical fibersrelative to each other while allowing the optical fibers to be highlyaccurately positioned relative to each other, and wherein any possibleadverse influence which may be brought about by rays of light reflectedfrom end faces of the optical fibers is minimized.

To this end, an optical fiber array according to the present inventioncomprises a pair of blocks having respective recesses which, when theblocks are combined together, cooperate together to define a cavity, anda plurality of optical fibers having respective end portionsaccommodated within the cavity in a linear array. Neighboring end facesof the blocks adjacent end faces of the optical fibers are groundslantwise relative to a common plane in which the linear array of theend portions of the optical fibers lie and also relative to an opticalaxis of each of the optical fibers.

According to one aspect of a method of making the optical fiber array ofthe present invention, the optical fiber array of the type referred toabove can be manufactured by preparing first and second blocks eachhaving a generally L-shaped recess defined therein and delimited by astep and a flat wall surface perpendicular to the step, in saidrespective first and second blocks defining the cavity when said firstand second blocks are combined together; placing end portions of theoptical fibers on the flat wall surface of the first block in a lineararray so as to dispose the linear array of the end portions of theoptical fibers in the recess of the first block; placing the secondblock over said one of the blocks with the inclined end faces of saidfirst and second blocks lying in a common plane and with the steps inthe first and second blocks situated on respective sides of the lineararray of end portions of the optical fibers; moving one of the first andsecond blocks relative to the other of the first and second blocks in adirection by which the steps of said first and second blocks are broughttowards each other so as to confine the linear array of the end portionsof the optical fiber within the cavity while the end portions of theoptical fibers are brought into a closely juxtaposed relationship witheach other; and grinding respective end faces of the optical fiberstogether with the end faces of the first and second blocks so as to alsobe inclined.

According to another aspect of the method of making the optical fiberarray of the present invention, a viscous liquid medium may be appliedto the end portions of the optical fibers after the placement of the endportions of the optical fibers on the flat wall surface of the firstblock.

Also, regardless of whether the viscous liquid medium is employed, thefirst and second blocks placed one above the other with the opticalfibers accommodated loosely within the cavity may be sandwiched betweenmagnets or between an electromagnet and a metal member to retain thefirst and second blocks in position relative to each other prior to oneof the first and second blocks being moved relative to the other of thefirst and second blocks.

The viscous liquid medium may be a UV-curable resin that can be curedupon being irradiated with UV rays of light.

The present invention also provides a wavelength selecting deviceutilizing the optical fiber array of the structure referred to above inwhich no harmful rays of light reflected backwards will enter an inputoptical fiber. This wavelength selecting device comprises a diffractiongrating, a lens, and the optical fiber array including an input opticalfiber and a light receiving optical fiber, respective end faces of theinput and light receiving optical fibers being inclined in the samedirection and disposed in a linear array in a direction parallel to thedirection in which the grating grooves extend in the diffraction gratingso as to lie parallel to each other.

Preferably, the diffraction grating may be a Fourier diffraction gratingcapable of exhibiting a high efficiency of diffraction and having aminimized dependency on polarized light, an example of which isdisclosed in Appl. Opt. 31, No. 16, pp. 3015-3019 (1992).

According to the present invention, since the respective end faces ofthe optical fibers are ground to be inclined in the same direction, raysof light reflected from the end faces of the optical fibers arereflected at an angle effective to avoid any possible re-entry thereofinto the original optical system. Also, if the input and light receivingoptical fibers forming parts of the wavelength selecting device arepositioned at respective locations different from the direction in whichthe rays of light are diffracted by the diffraction grating, no light ofunwanted wavelength will enter the input optical fiber.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withpreferred embodiments thereof with reference to the accompanyingdrawings, in which like parts are designated by like reference numeralsand in which:

FIG. 1 is a schematic perspective view of an optical fiber array;

FIG. 2 is a schematic front elevational view of the optical fiber arrayshown in FIG. 1;

FIG. 3 is a schematic perspective view of a block assembly used inmaking the optical fiber array;

FIGS. 4(a) to 7(d) are schematic diagrams showing the sequence of makingthe optical fiber array according to first to fourth preferredembodiments of the present invention;

FIGS. 8(a) and 8(b) are schematic diagram showing the sequence of makingthe prior art optical fiber array;

FIG. 9 is a schematic perspective view of the prior art optical fiberarray;

FIGS. 10(a) and 10(b) are schematic plan and side views of a wavelengthselecting device; and

FIGS. 11(a) and 11(b) are schematic plan and side views of the prior artwavelength selecting device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic perspective view of one preferred embodiment of anoptical fiber array according to the present invention and FIG. 2 is aschematic front elevational view of the optical fiber array. Referringto FIGS. 1 and 2, reference numerals 11 and 12 represent lower and upperblocks, respectively; reference numerals 21 and 22 represent stepsdefined in the respective blocks 11 and 12; reference numeral 3represents a plurality of optical fibers; and reference numerals 91 and92 represents end faces of the respective blocks 11 and 12 adjacentwhere respective end faces of the optical fibers 3 are situated. Asshown in FIG. 2, the optical fibers 3 are fixedly arranged in a lineararray with their end portions closely juxtaposed and firmly receivedbetween flat upper and lower wall surfaces of the blocks 11 and 12 andalso between the steps 21 and 22 of the blocks 11 and 12.

The respective end faces 91 and 92 of the blocks 11 and 12 adjacent endfaces of the optical fibers 3 are, as best shown in FIG. 1, ground fromabove so as to be inclined relative to the optical axes of the opticalfibers 3 so that a common plane in which the end faces 91 and 92 lie isinclined relative to the optical axes of the optical fibers 3, butparallel to the direction in which the optical fibers 3 are held in aclosely neighboring relationship with each other. Therefore, respectiveend faces of the optical fibers 3 are correspondingly ground and lieflush with the common plane in which the end faces 91 and 92 of theblocks 11 and 12 lie.

It will readily be understood that the end faces of the respectiveoptical fibers 3 are ground at an equal angle of inclination and,therefore, the resultant linear array of the optical fibers 3 iseffective to avoid any possible adverse influence which would otherwisebrought about on an optical element with which the optical fiber arrayis coupled.

According to the present invention, the above-described optical fiberarray can be fabricated by means of various methods which will now bedescribed.

FIG. 3 illustrates, in a schematic perspective view, a block assemblycomprising the upper and lower blocks 11 and 12 and FIGS. 4(a) to 4(c)illustrate the sequence of making the optical fiber array according to afirst preferred embodiment of the present invention. In FIGS. 3 and 4,reference numerals 11 and 12 represent lower and upper blocks,respectively; reference numerals 21 and 22 represent steps defined inthe respective blocks 11 and 12; reference numeral 3 represents aplurality of optical fibers; reference numerals 41 and 42 represent flatwall surfaces of the respective blocks 11 and 12 which cooperate withthe associated steps 21 and 22 to define generally L-shaped recesses,respectively; and reference numerals 91 and 92 represent end faces ofthe respective blocks 11 and 12 adjacent where respective end faces ofthe optical fibers 3 are situated.

Referring first to FIG. 4(a), the plural optical fibers 3 are positionedrelative to the block assembly with their end portions placed on theflat wall surface 41 of the lower block 11. Each of the lower and upperblocks 41 and 42 has an inclined end face 91 and 92 as shown in FIG. 3,and, when the end portions of the respective optical fibers 3 are placedon the flat wall surface 41 of the lower block 11, they need not bebrought into contact with each other.

Thereafter, the upper block 12 having a structure similar to that of thelower block 11, i.e. a recess delimited by the step 22 and the flat wallsurface 42, is placed over the lower block 11 as shown in FIG. 4(b) witha linear array of the end portions of the optical fibers 3 confinedwithin a cavity defined by the recesses in the lower and upper blocks 11and 12. As clearly shown in FIG. 4(b), the placement of the upper block12 over the lower block 11 is carried out such that the steps 21 and 22in the lower and upper blocks 11 and 12 occupy positions on respectivesides of the linear array of the end portions of the optical fibers 3while the flat wall surfaces 41 and 42 thereof contact the individualend portions of the optical fibers 3 to sandwich the linear arraythereof. If the height of each step 21 and 22 is chosen to be smallerthan the outer diameter of each of the optical fibers 3, the flat wallsurface 41 and 42 of each lower and upper block 11 and 12 are alwaysheld in contact with the optical fibers 3 upon placement of the upperblock 12 over the lower block 11.

After the placement of the upper block 12 over the lower block 11 asshown in FIG. 4(b), one of the lower and upper blocks, for example, theupper block 12 is moved parallel relative to the lower block 11 in adirection transverse to the optical axes of the optical fibers 3 asshown by the arrow in FIG. 4(b) to bring the step 22 towards the step 21and hence to bring the end portions of the optical fibers 3 into aclosely neighboring relationship with each other as shown in FIG. 4(c).In this condition of FIG. 4(c), neighboring end portions of the opticalfibers 3 are held in contact with each other while the outermost andportions are also held in contact with the respective steps 21 and 22 inthe lower and upper blocks 11 and 12.

The lateral movement of the upper block 12 relative to the lower block11 is terminated when the end portions of the optical fibers 3 arebrought into the closely neighboring relationship as shown in FIG. 4(c),and the lower and upper blocks 11 and 12 are then fixed together withthe linear array of the optical fibers firmly clamped therebetween.After this fixing, the respective end faces 91 and 92 of the lower andupper blocks 11 and 12 where respective end faces of the optical fibers3 are situated are ground at an inclination thereby completing theoptical fiber array as shown in FIG. 1.

According to the foregoing method of the present invention, since theplural optical fibers are positioned between the two blocks each havinga recess defined therein and are then brought into a closely neighboringrelationship with each other by a lateral movement of one of the blocksrelative to the other, the end faces of the optical fibers can beuniformly ground until inclined while in a linearly juxtaposedrelationship with each other by means of a simple technique. Moreover,each of the blocks having the respective recesses defined therein canreadily and easily be manufactured with no substantially complicatedprocedure required.

Reference will now be made to FIG. 5 showing a second preferredembodiment of the method according to the present invention. In thepractice of this method, two magnets 5 are employed. While the methodshown in FIG. 5 is similar to that according to the foregoing embodimentof the present invention, after the placement of the end portions of theoptical fibers 3 over the lower block 11 as shown in FIG. 5(a) followedby the placement of the upper block 12 over the lower block 11substantially as shown in FIG. 5(b), the lower and upper blocks 11 and12 are temporarily retained in position sandwiching a loose array ofthose end portions of the optical fibers 3 by means of the magnets 5then exerting magnetic forces of attraction that act to draw the lowerand upper blocks 11 and 12 close towards each other as shown in FIG.5(b).

After the condition of FIG. 5(b), the upper block 12 is moved relativeto the lower block 11 in a manner similar to that effected in thepractice of the foregoing embodiment of the present invention until theend portions of the optical fibers 3 are brought into the closelyneighboring relationship as shown in FIG. 5(c), and the lower and upperblocks 11 and 12 are then fixed together with the linear array of theoptical fibers firmly clamped therebetween. After this fixing, therespective end faces 91 and 92 of the lower and upper blocks 11 and 22where respective end faces of the optical fibers 3 are situated areground until skewed thereby completing the optical fiber array.

According to the second embodiment of the present invention, the pluraloptical fibers are positioned between the two blocks each having arecess defined therein and are then brought into a closely neighboringrelationship with each other by a lateral movement of one of the blocksrelative to the other while the blocks are sandwiched between themagnets. Therefore, the end faces of the optical fibers can be uniformlyground until inclined while in a linearly juxtaposed relationship witheach other by means of a simplified technique. Moreover, each of theblocks having the respective recesses defined therein can readily andeasily be manufactured with no substantially complicated procedurerequired.

FIG. 6 illustrates a third preferred embodiment of the method accordingto the present invention. This method differs from the second embodimentof the present invention in that, in the practice of the method shown inFIG. 5, a viscous liquid medium 6 is employed.

As shown in FIG. 6(a), the plural optical fibers 3 are positionedrelative to the block assembly with their end portions placed on theflat wall surface 41 of the lower block 11. When the end portions of therespective optical fibers 3 are placed on the flat wall surface 41 ofthe lower block 11, they need not be brought into contact with eachother. Thereafter, the viscous liquid medium 6 is applied over those endportions of the optical fibers 3 resting on the flat wall surface 41 ofthe lower block 11.

The upper block 12 similar the lower block 11 is then placed over thelower block 11 as shown in FIG. 6(b) with a linear array of the endportions of the optical fibers 3 confined within a cavity defined by therecesses in the lower and upper blocks 11 and 12. The placement of theupper block 12 over the lower block 11 is carried out such that thesteps 21 and 22 in the lower and upper blocks 11 and 12 occupy positionson respective sides of the linear array of the end portions of theoptical fibers 3 while the flat wall surfaces 41 and 42 thereof contactthe individual end portions of the optical fibers 3 to sandwich thelinear array thereof. At this time, due to the viscosity of the liquidmedium 6, the upper block 12 so placed is spaced from the end portionsof the optical fibers 3 and also from the lower block 11. The placementof the upper block 12 over the lower block 11 is followed by a placementof the magnets 5 with the blocks 11 and 12 positioned therebetween asshown in FIG. 6(b).

After the placement of the magnets 5, the upper block 12 is movedparallel relative to the lower block 11 in a direction transverse to theoptical axes of the optical fibers 3 as shown by the arrow in FIG. 6(b)to bring the step 22 towards the step 21 and hence to bring the endportions of the optical fibers 3 into a closely neighboring relationshipwith each other as shown in FIG. 6(c). The lateral movement of the upperblock 12 relative to the lower block 11 is terminated when that endportions of the optical fibers 3 are brought into the closelyneighboring relationship. In this condition of FIG. 6(c), neighboringend portions of the optical fibers 3 are held in contact with each otherwhile the outermost end portions are also held in contact with therespective steps 21 and 22 in the lower and upper blocks 11 and 12.

Once the condition as shown in FIG. 6(c) has been established, theviscous liquid medium 6 filling the gap between the lower and upperblocks 11 and 12 is partially squeezed outwardly from lateral faces ofthe blocks 11 and 12 by a compressive force developed as a result of themagnetic forces of attraction acting between the magnets 5, therebyconfining the end portions of the optical fibers within the cavitybetween the blocks 11 and 12 in a linear array as shown in FIG. 6(d).

After the fixing, the respective end faces 91 and 92 of the lower andupper blocks 11 and 22 where respective end faces of the optical fibers3 are situated are ground at an inclination thereby completing theoptical fiber array.

According to the third embodiment of the present invention, the use ofthe viscous liquid medium 6 is effective to disperse stresses which areproduced by the blocks 11 and 12 on the end portions of the opticalfibers during the arrangement thereof in a linear array, making itpossible to provide the optical fiber array at a high yield.

The fourth preferred embodiment of the method of making the opticalfiber array according to the present invention is shown in FIG. 7. Themethod shown in FIG. 7 is generally similar to a combination of thesecond and third embodiments of the present invention, except that inplace of the magnets 5 used in the practice of the third embodiment ofthe present invention a combination of an electromagnet 51 and a metalblock 8 made of, for example, iron is employed.

Specifically, as shown in FIG. 7(a), the plural optical fibers 3 arepositioned relative to the block assembly with their end portions placedon the flat wall surface 41 of the lower block 11. When the end portionsof the respective optical fibers 3 are placed on the flat wall surface41 of the lower block 11, they need not be brought into contact witheach other. Thereafter, the viscous liquid medium 6 is applied overthose end portions of the optical fibers 3 resting on the flat wallsurface 41 of the lower block 11. The upper block 12 is then placed overthe lower block 11 as shown in FIG. 7(b) with a linear array of the endportions of the optical fibers 3 confined within a cavity defined by therecesses in the lower and upper blocks 11 and 12. The placement of theupper block 12 over the lower block 11 is carried out such that thesteps 21 and 22 in the lower and upper blocks 11 and 12 occupy positionson respective sides of the linear array of the end portions of theoptical fibers 3 while the flat wall surfaces 41 and 42 thereof contactthe individual end portions of the optical fibers 3 to sandwich thelinear array thereof. At this time, due to the viscosity of the liquidmedium 6, the upper block 12 so placed is spaced from the end portionsof the optical fibers 3 and also from the lower block 11. The placementof the upper block 12 over the lower block 11 is followed by a placementof the electromagnet 51 and the metal block 8 with the blocks 11 and 12positioned therebetween as shown in FIG. 7(b).

After the placement of the electromagnet 5 and the metal block 8, theupper block 12 is moved parallel relative to the lower block 11 in adirection transverse to the optical axes of the optical fibers 3 asshown by the arrow in FIG. 7(b) to bring the step 22 towards the step 21and hence, to bring the end portions of the optical fibers 3 into aclosely neighboring relationship with each other as shown in FIG. 7(c).The lateral movement of the upper block 12 relative to the lower block11 is terminated when the end portions of the optical fibers 3 arebrought into the closely neighboring relationship. In this condition ofFIG. 7(c), neighboring end portions of the optical fibers 3 are held incontact with each other while the outermost end portions are also heldin contact with the respective steps 21 and 22 in the lower and upperblocks 11 and 12.

Once the condition as shown in FIG. 7(c) has been established, aprogressively increasing electric voltage is applied from an electricpower source 7 to the electromagnet 51 to cause the latter to exert amagnetic force of attraction acting to draw the metal block 8 towardsthe electromagnet 51 thereby compressing the blocks 11 and 12 togetherso that the viscous liquid medium 6 filling the gap between the lowerand upper blocks 11 and 12 is partially squeezed outwardly from lateralfaces of the blocks 11 and 12. In this way, the end portions of theoptical fibers are confined within the cavity between the blocks 11 and12 in a linear array as shown in FIG. 7(d).

After the fixing, the respective end faces 91 and 92 of the lower andupper blocks 11 and 22 where respective end faces of the optical fibers3 are situated are ground at an inclination thereby completing theoptical fiber array.

According to the fourth embodiment of the present invention, the use ofthe electromagnet 51 is effective to speed the squeezing of the viscousliquid medium 6, which results in the shortening of manufacturing time.

According to the fourth embodiment of the present invention, the use ofthe viscous liquid medium 6 is effective to disperse stresses which areproduced by the blocks 11 and 12 on the end portions of the opticalfibers during the arrangement thereof in a linear array, and those endportions of the optical fibers confined within the cavity are favorablyclosely juxtaposed with each other.

It is to be noted that if in the practice of any one of the third andfourth embodiments of the present invention the viscous liquid medium 6is employed in the form of a UV-curable resin, the assembly shown inFIG. 6(d) or FIG. 7(d) should be exposed to UV radiation to fix thelinear array of the optical fibers. In this case, one or both of thelower and upper blocks must be made of material transparent to the UVrays of light.

Also, if each of the lower and upper blocks 11 and 12 is made ofmaterial having a hardness equal to that of the optical fibers employed,for example, glass, the block assembly consisting of the lower and upperblocks can easily be ground and the end faces of the optical fibersretained by the block assembly can readily be ground simultaneously to adesired finish.

As hereinbefore described, by grinding the end faces of the opticalfibers, arranged in a linear array between the blocks having therespective recesses each delimited by the step and the flat wallsurface, along the inclined end faces of the respective blocks, the endfaces of the optical fibers can be uniformly ground at an angle ofinclination conforming to the angle of inclination of a common plane inwhich the end faces of the respective blocks lie. In the resultantoptical fiber array, the end portions of the optical fibers are veryclosely juxtaposed with each other, arranged in a linear array andpositioned accurately. Also, the use of the viscous liquid medium iseffective to disperse the stresses, to avoid any possible breakage ofsome of the optical fibers during the arrangement and to provide theresultant optical fiber array at a high yield. When the UV-curable resinis employed for the viscous liquid medium, the optical fibers canreadily and easily be fixed in position relative to each other.

An embodiment of the wavelength selecting device utilizing the opticalfiber array of the structure discussed hereinbefore will now bedescribed.

FIG. 10 illustrates the structure of the wavelength selecting device,wherein FIGS. 10(a) and 10(b) are top plan and side views, respectively.Referring now to FIG. 10, reference numeral 101 represents an inputfiber; reference numeral 102 represents a light receiving fiber;reference numeral 103 represents a lens; reference numeral 104represents a diffraction grating; reference numeral 105 represents arotary mechanism; reference numeral 106 represents an end face where endfaces of the optical fibers are situated; and reference numeral 107represents an optical fiber array in which the input and light receivingfibers 101 and 102 are arranged. For the purpose of discussion, thewavelengths are respectively designated by λa, λb and λc in the orderfrom the shortest wavelength.

The wavelength selecting device operates in the following manner.

Wavelength multiplexed beams having the respective wavelengths λa, λband λc emitted from the input optical fiber 101 are incident on thediffraction grating 104 through the lens 103 and are subsequentlydiffracted by the diffraction grating 104 at different angles. Thediffraction grating 104 is rotated by the rotary mechanism 106 about anaxis of rotation parallel to grating grooves in the diffraction grating104 so as to assume such an angle that, for example, the wavelength λican be coupled with the light receiving fiber 102 through the lens 103.If the preset angle as viewed in a direction conforming to the normal ofthe diffraction grating 104 is θi and the interval between each ofneighboring grating grooves in the diffraction grating 104 is d, thepreset angle θi can be expressed by the following equation:

    θi=sin.sup.-1 (λi/2d) {i=a, b, c}             (1)

and in such construction, θa<θb<θc. Each of the input and lightreceiving optical fibers 101 and 103 has an end face 106 inclined in thesame direction and is laid down with its lengthwise direction inclinedrelative to the axis of beam at an angle dependent on the angle ofinclination of the respective end face of each optical fiber. If theangle of inclination of the optical fibers relative to an optical axisis expressed by δ, the index of refraction of the optical fiber isexpressed by n_(g) and the angle of inclination of the end face relativeto the normal of the optical axis of each of the optical fibers isexpressed by φ, the following equation can be obtained.

    δ=sin.sup.-1 (n.sub.g sin φ)-φ               (2)

In order for the optical fibers 101 and 102 to have their end faces 106ground in the same inclined direction, the optical fiber array 107including block surface 106 has been ground to be inclined while theoptical fibers 101 and 102 are sandwiched as shown in FIG. 10(a), shouldbe employed. With this construction, by fixing the optical fiber array107 to a jig that will establish the angle δ of inclination relative tothe optical axis of the optical fiber, the optical fibers 101 and 102can be disposed at the same angle δ of inclination.

As hereinabove described, according to the present invention, the raysof light returning from an optical system back to the end faces of theinput and light receiving optical fibers can be reflected at an anglethat satisfies the following equation and can therefore be preventedfrom returning to the optical system:

    φ=2(δ+φ)                                     (3)

wherein φ represents the angle of reflection of the rays of lightrelative to the optical axis.

Preferably, the angle φ at which the end face of each of the opticalfibers is ground at an inclination is generally within the range of 7 to9 degrees. Accordingly, the angle δ of inclination is within the rangeof 3.5 to 4 degrees.

The input and light receiving optical fibers 101 and 102 are arranged inthe same direction as that of the grating grooves in the diffractiongrating 104 as shown in FIGS. 10(a) and 10(b). Thus, the wavelengthmultiplexed beams emerging from the input optical fiber 101 can bedispersed along a linear line perpendicular to the direction of thegrating grooves and intersecting the light receiving optical fiber 102and, therefore, an optical system can be realized in which no dispersedrays of light return to the input optical fiber 101. This can beaccomplished by arranging the optical fiber array 107 in a manner asshown in FIG. 11(b).

It is to be noted that, while in the illustrated embodiment the opticalfibers 101 and 102 have been described as arranged in the same directionas that of the grating grooves, any relative positioning may be employedprovided that no rays of light dispersed from the diffraction grating104 will return to the input optical fiber 101.

Although reference has been made to the use of the diffraction grating,if a Fourier diffraction grating which is generally known as a highefficient diffraction grating having a minimized dependency on polarizedlight is employed, the proportion of the diffracted rays of light, thatis, the efficiency of diffraction, amounts to 90% or higher and,therefore the intensity of light coupled with the light receivingoptical fiber can be enhanced. Furthermore, since the inclined end faceslie in the same direction, the input and light receiving optical fiberscan be retained in the same direction and can therefore goodreproductivity can be attained.

As hereinbefore discussed, since according to the present invention therespective end faces of the input optical fiber and the light receivingoptical fibers are ground inclined in the same direction, no reflectedlight returns to the optical system and the relative positioning canreadily be accomplished.

It is to be noted that the optical fiber array of the present inventioncan be utilized with no distinction made between the input and lightreceiving features and the present invention can be applicable to anoptical system which requires a plurality of inputs and outputs from anoptical device taking the shape of an array.

Although the present invention has been described in connection with thepreferred embodiments thereof with reference to the accompanyingdrawings, it is to be noted that various changes and modifications willbecome apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless theyotherwise depart therefrom.

What is claimed is:
 1. A method of making an optical fiber array whichcomprises the steps of:preparing first and second blocks each having agenerally L-shaped recess defined therein, each of said blocks having astep and a flat wall surface perpendicular to the step which delimitsaid recess, said recesses in said respective first and second blocksdefining a cavity when said first and second blocks are placed togetherin a mating relation, neighboring end faces of said first and secondblocks being oblique to said flat wall surfaces; placing end portions ofoptical fibers on the flat wall surface of the first block in a lineararray so as to dispose the linear array of the end portions of theoptical fibers in the recess of the first block; placing the secondblock over said first block with the inclined end faces of said firstand second blocks lying in a common plane and with the steps of thefirst and second blocks situated on respective sides of the linear arrayof the end portions of the optical fibers; moving one of the first andsecond blocks relative to the other of the first and second block in adirection which brings the steps of said first and second blocks towardseach other so as to confine the linear array of the end portions of theoptical fibers within the cavity while the end portions of the opticalfibers are brought into a closely juxtaposed relationship with eachother; and grinding the end faces of the optical fibers together withthe end faces of the first and second blocks in such a manner that theend faces of the first and second blocks and the end faces of theoptical fibers lie in a common plane inclined relative to a plane inwhich the linear array of the optical fibers lie and to an optical axisof each of the fibers.
 2. A method of making the optical fiber array asclaimed in claim 1, wherein the step of preparing comprises preparingeach of said first and second blocks from a material having a hardnessequal to that of the optical fibers.
 3. A method of making an opticalfiber array which comprises the steps of:preparing first and secondblocks each having a generally L-shaped recess defined therein, each ofsaid blocks having a step and a flat wall surface perpendicular to thestep which delimit said recess, said recesses in said respective firstand second blocks defining a cavity when said first and second blocksare placed together in a mating relation, neighboring end faces of saidfirst and second blocks being oblique to said flat wall surfaces;placing end portions of optical fibers on the flat wall surface of thefirst block in a linear array so as to dispose the linear array of theend portions of the optical fibers in the recess of the first block;placing the second block over said first block with the inclined endfaces of said first and second blocks lying in a common plane and withthe steps of the first and second blocks situated on respective sides ofthe linear array of the end portions of the optical fibers; disposingfirst and second magnets on respective sides of an assembly of the firstand second blocks so that the first and second blocks are retained inposition by a magnetic force of attraction acting between the first andsecond magnets; moving one of the first and second blocks relative tothe other of the first and second block in a direction which brings thesteps of said first and second blocks towards each other so as toconfine the linear array of the end portions of the optical fiberswithin the cavity while the end portions of the optical fibers arebrought into a closely juxtaposed relationship with each other; andgrinding the end faces of the optical fibers together with the end facesof the first and second blocks in such a manner that the end faces ofthe first and second blocks and the end faces of the optical fibers liein a common plane inclined relative to a plane in which the linear arrayof the optical fibers lie and to an optical axis of each of the fibers.4. A method of making the optical fiber array as claimed in claim 3,wherein the step of preparing comprises preparing each of said first andsecond blocks from a material having a hardness equal to that of theoptical fibers.
 5. A method of making an optical fiber array whichcomprises the steps of:preparing first and second blocks each having agenerally L-shaped recess defined therein, each of said blocks having astep and a flat wall surface perpendicular to the step which delimitsaid recess, said recesses in said respective first and second blocksdefining a cavity when said first and second blocks are placed togetherin a mating relation, neighboring end faces of said first and secondblocks being oblique to said flat wall surfaces; placing end portions ofoptical fibers on the flat wall surface of the first block in a lineararray so as to dispose the linear array of the end portions of theoptical fibers in the recess of the first block; applying a viscousliquid medium into the recess of the first block and onto the endportions of the optical fibers accommodated therein; placing the secondblock over said first block with the inclined end faces of said firstand second blocks lying in a common plane and with the steps of thefirst and second blocks situated on respective sides of the linear arrayof the end portions of the optical fibers; disposing first and secondmagnets on respective sides of an assembly of the first and secondblocks so that the first and second blocks are retained in position by amagnetic force of attraction acting between the first and secondmagnets; moving one of the first and second blocks relative to the otherof the first and second block in a direction which brings the steps ofsaid first and second blocks towards each other so as to confine thelinear array of the end portions of the optical fibers within the cavitywhile the end portions of the optical fibers are brought into a closelyjuxtaposed relationship with each other; and grinding the end faces ofthe optical fibers together with the end faces of the first and secondblocks in such a manner that the end faces of the first and secondblocks and the end faces of the optical fibers lie in a common planeinclined relative to a plane in which the linear array of the opticalfibers lie and to an optical axis of each of the fibers.
 6. A method ofmaking the optical fiber array as claimed in claim 5, wherein the stepof disposed comprises disposing electromagnets on the respective sidesof the assembly and applying an electric voltage to said electromagnets.7. A method of making the optical fiber array as claimed in claim 5,wherein the step of applying said viscous liquid medium comprisesapplying a UV-curable resin and further comprising curing the UV-resinby radiating the linear array of the end portions of the optical fiberswith UV-rays of light to thereby fix the linear array in position.
 8. Amethod of making the optical fiber array as claimed in claim 5, whereinthe step of preparing comprises preparing the first and second blocksfrom a material transparent to UV-rays of light.
 9. The method of makingthe optical fiber array as claimed in claim 5, wherein the step ofpreparing comprises preparing each of said first and second blocks froma material having a hardness equal to that of the optical fibers.